[Arran]

Greetings;
I think I may have found a clue as to what is missing, from a search I made, there is a rear view of the chassis in the second photo on this page showing a stiff piece of wire connected to the flag/semaphore behind the dial, presumably that is what connects the volume control to the flag: https://www.radiomuseum.org/r/philco_40_100.html

According to the instruction book, scanned and posted in our own Philcoradio library, the wire piece is called a "Flag Arm Transfer Lever Assembly" though it does not show the part.

https://philcoradio.com/library/index.ph...tructions/

Anyhow have you removed the chassis from the cabinet yet, there is a chance that this piece may have fallen off in the back somewhere? If not it does not look like it would be too hard to replicate if someone could furnish a picture. I should also mention that Philcos in this era used a lot of rubber/gutta percha covered wire, and they may have used the same in the battery cables, if they look deteriorated in any way, especially where they enter the chassis, DO NOT attempt to power the set up. All that it takes is a short from the 90 volt B+ to the 1.4 volt filaments, and you will instantly need a new set of tubes.
Regards
Arran